The carbon isotope composition of C_3 herbaceous plants in loess area of northern China   总被引：9，自引：0，他引：9  

王国安  韩家懋  刘东生 《中国科学D辑(英文版)》2003,46(10)

The application of stable carbon and oxygen isotopes in study of paleoenvironment has been becoming more and more extensive. It is well known that the d 18O curves of foraminifer crust in deep oceanic sediments and ice cores have made a great contribution…  相似文献   

DISTRIBUTIONS AND VARIATIONS OF SURFACE OZONE IN CHANGSHU, YANGTZE DELTA REGION^*          下载免费PDF全文

YAN Peng  WANG Mulin  CHENG Hongbing  ZHOU Xiuji 《Acta Meteorologica Sinica》2003,17(2):205-217

Through one and half year continuous in-situ measurements,the distributions and variations of surface ozone and its precursors at a typical mixed agricultural and metropolitan area-Changshu,Yangtze Delta region,were studied.The preliminary analysis on the concentration levels and variations of surface ozone indicated the obvious seasonal and diurnal cycles during the experiment.The hourly averaged concentrations of surface ozone were high,in about 17% of total valid hours the surface ozone concentration exceeded 50 ppb,and in 22 days the hourly averaged ozone concentration was greater than 100 ppb.There were about 40% of the days in that the daily maximum 8-hour ozone concentration was greater than 50 ppb.The days with daily maximum 8-hour ozone concentration greater than 80 ppb were about 33 days that accounted for about 8% of the observational days.The variations of 5-day moving averaged ozone concentrations depended both on the weather conditions and on the changes of ozone in background atmosphere.Photochemical process had the significant impacts on ozone productions.  相似文献   

Saguaro Distribution under Nurse Plants in Arizona's Sonoran Desert: Directional and Microclimate Influences*     

Taly D. Drezner  Colleen M. Garrity 《The Professional geographer》2003,55(4):505-512

The saguaro cactus, an icon of the American southwestern desert, defines the extent of the Sonoran Desert through portions of its range. Saguaros rely upon nurse plants for establishment and survival in the harsh temperature and moisture regime of the desert. Freezing temperatures limit the range of the saguaro to the north in Arizona. However, nurse plants extend the range of saguaros by providing more moderate conditions beneath their canopies. This study focuses on precisely these small, highly localized temperature variations, which, we suggest, are linked to regional‐scale patterns of distribution of the species, particularly in marginal, cold‐limited locales. We sampled 291 saguaros over thirty populations in Arizona, in the northern portion of their range. Saguaros establish under the south side of their nurse's canopy in the coldest parts of their range more often than expected, while a significant distributional bias is not observed in those in warmer, more moderate plots. To further investigate air temperature as a possible factor in the directional bias of saguaro establishment, we collected microclimate data under the north and south sides of the canopies of two common nurse plants, Cercidium microphyllum (a tree) and Ambrosia deltoidea (a shrub) in Phoenix, Arizona. South sides of nurses have significantly higher minimum temperatures than do the north sides. Survivorship in the coldest areas appears to be greatest under the south side of a nurse's canopy, where warmer wintertime microclimatic conditions occur. We suggest that within‐canopy microclimatic variability under a single nurse plant may be reflected in regional distributional and in the survivorship patterns of saguaros throughout Arizona.  相似文献   

The rise of trees and their effects on Paleozoic atmospheric CO₂ and O₂     

Robert A. Berner 《Comptes Rendus Geoscience》2003,335(16):1173-1177

The rise of large vascular plants during the mid-Paleozoic brought about a major increase in the rates of weathering of silicate minerals that induced a drop in the level of atmospheric CO₂ and contributed, via the atmospheric greenhouse effect, to global cooling and the initiation of the most long lived and a really extensive glaciation of the past 550 million years. Sedimentary burial of the microbiologically resistant remains of the plants resulted during the Permo-Carboniferous in both further lowering of CO₂ and in elevation of atmospheric O₂. Evidence of changes in CO₂ and O₂ are provided by mathematical models, studies of paleosols, fossil plants, fossil insects, and the effects of modern plants on silicate weathering, and by laboratory studies of the effects of changes in O₂ on plants and insects. To cite this article: R.A. Berner, C. R. Geoscience 335 (2003).  相似文献   

利用水系沉积物地球化学数据判别浅覆盖区岩性与构造--欧氏距离法   总被引：3，自引：2，他引：3  

时艳香  纪宏金  郝立波  陆继龙 《物探化探计算技术》2004,26(3):243-246

针对浅覆盖区地质调查困难，缺少可对比已知资料的实际问题，这里以大兴安岭阿龙山地区1：250000水系沉积物资料为例，给出了浅覆盖区岩性和构造识别的一种方法。该方法依据水系沉积物对原岩的继承性，以不同岩性所对应的典型土壤为已知样品，采用欧氏距离作为分类指标，将研究区划分为不同的岩性类。得到的区域地球化学分类图反映了一定的岩性分布及构造特点，为区域地质调查提供了线索。  相似文献   

夏季欧亚中高纬持续流型特征Ⅱ:年代际变化和外源强迫   总被引：1，自引：0，他引：1       下载免费PDF全文

潘婕  彭京备  王盘兴  纪立人 《气象科学》2004,24(3):253-260

在“夏季欧亚中高纬持续流型特征Ⅰ：流型指数与持续流型”的基础上，分析了夏季欧亚中高纬流型指数的年代际变化特征．讨论了流型指数年代际变化与我国降水年代际变化之间的联系，并初步探讨了加热场和海温异常的影响。结果表明：(1)夏季欧亚中高纬流型指数有明显的年代际变化．且与我国江淮流域、华北的降水分别有相反的相关关系；(2)外源强迫对夏季中高纬度持续环流及其年代际变化的作用是不可忽视的。  相似文献   

塔里木盆地西南坳陷周边山前的典型构造模式建立     

姚卫江  陈文利  肖燕  王晓 《新疆地质》2002,20(Z1):47-50

塔里木盆地西南坳陷夹持于西昆仑与南天山褶皱带间,边界受大型逆冲推覆断裂带和走滑断裂带控制.塔西南坳陷经历了多期构造运动,其中以喜山期构造运动最为重要,地震资料反映的多层次滑脱主要为喜山期构造运动结果,其现今构造格局是逆冲推覆、滑脱、走滑共同作用的结果.塔西南坳陷构造变形复杂,尤其在其周边表现得更为明显.  相似文献   

沙尘暴形成史初步研究——中国沙漠几个典型地质学记录的实证   总被引：1，自引：0，他引：1  

李保生  安芷生  祝一志  靳鹤龄  周卫健  董光荣  高尚玉  吕玉晓  余雪飞  高全洲 《地学前缘》2002,9(3):189-200

以位于沙漠黄土边界带的榆林、阿羌和米浪沟湾地层剖面为典型例证 ,讨论了 110 0kaBP以来中国沙漠沙尘暴的形成、发展和演化过程。提出在过去的 110 0ka中该区总共记录了 4 2个沙尘暴时期 ,并与 4 1个间沙尘暴时期构成比较连续且交替进行的一系列沉积演化历史。其中 ,最强烈的沙暴期发生时间大致在 6 2 0kaBP和 6 80kaBP前后 ,最温暖的间沙尘暴期出现在 5 90～ 5 0 0kaBP和15 0～ 70kaBP。研究认为 ,110 0kaBP以来因沙尘暴期与间沙尘暴期交替出现而形成的沉积旋回 ,是自那时以来在冰期、间冰期气候波动影响下冬夏古代季风相互对峙、交替演化形成气候旋回的结果  相似文献   

大亚湾核电站建筑物变形规律的研究     

李勇  杨军元 《华东地质学院学报》2001,24(1):76-78

通过广东大亚湾核电站建筑物的几次实地变形监测，以及收集到的有关变形监测资料，经过数据处理与变形分析，总给出大亚湾核电站建筑物的变形规律。结果表明：核电站是安全的，其水平位移、沉降量符合客观规律，属正常的形变，为今后解决核电站建筑物变形观测问题提供了可靠的依据。  相似文献   

古植代陆地维管植物的多样性演化和绝灭     

李中明 《地质论评》1994,40(3)

本文描述了石炭—二叠纪陆地维管植物在物种、生态和遗传方面的多样性。并根据古生代末这些植物在时空上的演化过程和数量统计数字,确认二叠—三叠纪集群绝灭事件同样在植物中存在。进而还探讨了植物集群绝灭事件发生的原因,笔者认为其直接外部原因,可能是局部地质事件(如:构造活动、火山爆发)引起热带雨林大面积消失,使气候变干旱所致。又根据当今对化石植物生殖生物学的研究结果,认为当时大部分植物(即古植代植物)的生殖方式较单一,胚在发育时无休眠期,成熟的胚缺少良好的保护结构,不适合在干旱环境下传种繁殖是这次植物集群绝灭事件发生的主要内部原因。  相似文献